OK, Octopus Go & Octopus Agile are not actual tariffs, they’re kinda experimental, so when I signed up a few months back following the links to Octopus Agile it gave me the Octopus Direct fixed tariff for 12m & said that they would switch me to Agile once they had some half-hour smart meter readings to see if they could get reliable data. The critical thing is that they can get the usage for each half-hour period so they can charge you properly. I have a SMETS 2 meter so it only took two or three weeks before “The Octopus went Agile!”, I’d assume similar timescale for Octopus Go. The other thing that you probably don’t know yet is that there are also Octopus Go Faster tariffs where the cost could be say 5.5p/kWh for 5 hours instead of the 4 hours with Go, and the time period covered could start at say 8:30 in the evening if you’re lucky. You could likely switch on to an Octopus Go Faster tariff at some time in the future if you fancied cheap electric at a different time.
I changed my Electric and Gas to Octopus November 2018, then updated to Octopus Go tariff in January 2020, the whole transaction was seamless to date including the meter changes, I am still approximately £20 a month better off than my old supplier Southern Electric even with charging up my PHEV.
For some reason we cannot get the Octopus Go faster rate in our area, just the Go rate, I am not brave enough to us the Agile rate
Unfortunately I have suffered a brain injury and occasionally I get confused and often say the wrong thing.